title: Coherent topological transport on the surface of Bi₂Se₃.
abstract: The two-dimensional surface of the three-dimensional topological insulator is in the symplectic universality class and should exhibit perfect weak antilocalization reflected in positive weak-field magneto-resistance. Previous studies in topological insulator thin films suffer from high level of bulk n-type doping making quantitative analysis of weak antilocalization difficult. Here we measure the magneto-resistance of bulk-insulating Bi2Se3 thin films as a function of film thickness and gate-tuned carrier density. For thick samples, the magnitude of weak antilocalization indicates two decoupled (top and bottom) symplectic surfaces. On reducing thickness, we observe first a crossover to a single symplectic channel, indicating coherent coupling of top and bottom surfaces via interlayer tunnelling, and second, a complete suppression of weak antilocalization. The first crossover is governed by the ratio of phase coherence time to the inter-surface tunnelling time, and the second crossover occurs when the hybridization gap becomes comparable to the disorder strength.
authors.affiliation: Department of Physics, Center for Nanophysics and Advanced Materials, University of Maryland, College Park, Maryland 20742-4111, USA.
authors.forename: Dohun
authors.initials: D
authors.lastname: Kim
authors.forename: Paul
authors.initials: P
authors.lastname: Syers
authors.forename: Nicholas P
authors.initials: NP
authors.lastname: Butch
authors.forename: Johnpierre
authors.initials: J
authors.lastname: Paglione
authors.forename: Michael S
authors.initials: MS
authors.lastname: Fuhrer